Nitrogen is abundant in the Earth’s atmosphere and is present in water in the forms of nitrate, nitrite, and ammonia. Plants use nitrogen as a nutrient to build proteins by tracking it in through their root system. This is why it is important to test soil and irrigation water to determine the optimal level of nitrogen fertilization to obtain the best crop response and avoid over-fertilization. Nitrate-nitrogen tests can be performed year-round, but testing is particularly recommended during spring and late spring, when rainfall and temperature-related bursts of microbiological activity often have great influence on the availability of nitrate-nitrogen.
Nitrate is measured in drinking water. The EPA has a maximum contaminant level 10 mg/L limit of Nitrate as Nitrogen (NO3-N). Similarly, the World’s Health Organization has a limit of 50 mg/L Nitrate (NO3-) in drinking water. Both values are close with the difference being the chemical form. 50 mg/L Nitrate is equivalent to 11.29 mg/L as Nitrate-Nitrogen. Nitrate is monitored due to the effect it has on the oxygen carrying capacity of blood. In infants, if formula is prepared with water that has a high level of nitrates then this can be toxic due to the conversion of nitrate to nitrite. The nitrite reacts with iron in hemoglobin to form methemoglobin. The methemoglobin reduces the blood capacity to carry oxygen resulting in a blue discoloration known as Blue Baby Syndrome or methemoglobinemia.
Hanna Instruments offers a wide variety of instrumentation for measuring nitrate. Products include benchtop and portable pH/ISE meters that can use a liquid membrane nitrate Ion-Selective Electrode (ISE) for direct measurement. Both benchtop and portable meters have the ion charge and molecular weight pre-programmed in order to take ion concentration measurements along with multiple units of measure. The benchtop meters have incremental methods built-in.
Hanna offers a variety of chemical based methods to measure nitrate. Available technologies include Spectrophotometer, benchtop and portable photometers, Checker HC, and chemical test kits. The Spectrophotometer and photometers can display nitrate as Nitrate or as Nitrate-Nitrogen. A marine version of the Checker HC allows for the measurement of nitrate in seawater for the maintenance of a saltwater aquarium.
Below are the most common products used for nitrate measurement.
Benchtop pH/ISE meters
Benchtop pH/ISE meters include two channel options, in which a pH probe can be connected to one channel and the nitrate ISE to the other. The benchtop meters have the ion charge and molecular weight pre-programmed for use with the nitrate ISE. The benchtop meters also have incremental methods pre-programmed including the known addition, known subtraction, analyte addition and analyte subtraction methods
Portable pH/ISE Meters
Portable pH/ISE allow the flexibility to perform an ISE measurement locations with limited space and can be easily stored when completed. Two models are available including one dedicated to the nitrate measurement while the other can accept other ISEs and has the ion charge and weight pre-programmed for the specific parameter.
The nitrate ISE is a liquid membrane sensing electrode made with an ionophore impregnated into PVC. The electrode functions as a sensor or ionic conductor and produces a potential change due to changes in the sample’s ion activity. When the ionic strength of the sample is fixed by the addition of ISA, the voltage is proportional to the concentration of nitrate ions in solution and the electrode follows the Nernst equation.
The Nitrate ISE is available as a combination version with both indicating half-cell and reference half-cell. It is also available as an indicating half-cell that will be used with a separate reference half-cell. The reference half-cell with the skirted cone geometry is the preferred version to use.
Solutions for nitrate measurement include ISE standards and ISA for calibration and measurement.
Other solutions include the CAL Check standards for verifying and, if needed, the calibration of our portable photometers. Each CAL Check standard is supplied with a Certificate of Analysis stating the accuracy and traceability of the standard.
Spectrophotometers are available that have nitrate method in several ranges pre-programmed into the meter. The spectrophotometer offers the highest precision due to the quality of the optical system that has a wavelength accuracy of +/- 1.5 nm. The spectrophotometer allows for custom methods to be used as well.
Benchtop photometers include multiparameter versions for water treatment, wastewater treatment, water conditioning, and nutrient analysis. Each photometer is customized to have the parameters used by a specific industry. All benchtop have a digital pH electrode input allowing it to be used as a traditional pH meter.
Single parameter portable photometers are available in two ranges. The portable photometers have a CAL Check feature that allows for performance verification, and if needed, recalibration using the CAL Check standards. The portable meters are available as a meter only or as a kit. The kit version includes a rugged carrying case and CAL Check standards.
Checker HC, like a chemical test kit, are reagent based design in which there is a color change based on concentration. The handheld colorimeters, like portable and benchtop instrumentation, use the Beer-Lambert principle to determine the color change. The change in color is not subjective as with using the naked eye.
Chemical Test Kits
Nitrate chemical test kits are available for basic water quality testing and for irrigation water and soil. Multiparameter chemical test kits that measure nitrate are also available in the Hanna Backpack Labs used as an education aid when studying Environmental and Marine Science topics.
Reagents for the photometers and Checker HC. Photometer reagents are available in 100 or 300 tests versions.
Accessories include the replacement nitrate module for the combination ISE and magnetic stirrers for mixing. Also available are spare cuvettes and caps for the photometers and Checker HC.